Japanese rescue workers with bulldozers and sniffer dogs yesterday scrabbled through the mud to find survivors from a landslide that buried houses after a powerful quake, as the death toll rose to 18.

Around 22 people are still unaccounted for in the small northern countryside town of Atsuma, where a cluster of dwellings were wrecked when a hillside collapsed with the force of the 6.6-magnitude quake, causing deep brown scars in the landscape.

"We've heard there are people still stuck under the mud, so we've been working around the clock but it's been difficult to rescue them," a Self-Defense Forces serviceman in Atsuma told public broadcaster NHK.

"We will take measures to find them quickly."

An elderly woman in Atsuma told NHK: "My relative is still buried under the mud and has not been found yet, so I couldn't sleep at all last night. There were also several aftershocks so it was a restless night."

Around 1.6 million households in the sparsely populated northern island of Hokkaido were still without power after the quake damaged a thermal plant supplying electricity to the region.

Industry minister Hiroshige Seko said that number should be reduced to 550,000 households yesterday.

"It will take about a week" before the largest thermal power plant recovers, "so during that period, we are sending power-generating vehicles to hospitals," Seko told reporters.